Resin compositions such as methacrylic ester polymers are produced by continuous polymerization in which a raw material monomer, a polymerization initiator and so on are continuously supplied to a reactor to be polymerized. As such continuous polymerization processes, there are known a continuous solution polymerization process using a solvent (or a dispersion medium, which also applies hereinafter) to conduct continuous polymerization, and a continuous bulk polymerization process using no solvent to conduct continuous polymerization.
In general, a continuous solution polymerization process is not efficient since use of a solvent causes a low productivity. In contrast, a continuous bulk polymerization process has an advantage of being able to produce a polymer composition efficiently since the polymerization is conducted without using a solvent. Practically, the continuous bulk polymerization, however, has various problems compared with the continuous solution polymerization, such as that reaction control is difficult due to high viscosity of a reaction mixture, and when an inner surface of a reactor is cooled to remove heat from a reaction system, this degrades quality of a polymer composition and thus of a resin composition obtained therefrom. Therefore, a process is proposed which uses a reactor of a complete mixing type, fully fills the reactor with liquid to exclude a gas phase part therefrom, and conducts continuous bulk polymerization under an adiabatic condition with no heat transfer to or from the outside (Patent Literature 1). Further, in order to assure such adiabatic condition, a continuous polymerization apparatus is proposed which controls a supply amount of a raw material monomer and a supply amount of a polymerization initiator so as to make a temperature in the reactor equal to a setting temperature of an outer surface of the reactor (Patent Literature 2).